Thermostats are one of many mass-produced products for the home which are considered to be essential for comfortable operation but which should not impart a significant cost to the user. Modern-day thermostats have a degree of accuracy and a simplicity of manufacture which are meeting all but the most complicated needs for heat and airconditioning control. Because of the simplicity of design, there are relatively few parts and operation can continue with reasonably acceptable accuracy for an indefinite but extensive period of time.
In order to achieve economy of installation, it has been found most efficient to calibrate the thermostat at the point of manufacture. This is particularly true in case of thermostats which employ a bimetal coil of metals which expand or contract as the temperature changes and which actuate a switch at a predetermined temperature. In many instances, the switch is a simple mercury switch which gives a positive open and closed response with the degree of accuracy desired for maintenance of home temperature and airconditioning. This bimetal temperature sensing means is adjustable in the home or other place of use over a relatively narrow range of temperature. To insure that the bimetal material functions properly within this very narrow temperature range, the position of the coil is adjusted at the factory to give adequate response in conjunction with the switch. Thus the thermostat may be attached to the wall of the room being controlled and connected to the electrical circuit without extensive calibration by a service man at the time of installation.
One major problem in shipping precalibrated thermostats for installation is that it is possible for the calibration to be inadvertently changed. On the site, calibration of a thermostat which is badly out of adjustment can sometimes cost more than the device itself. If this adjustment is done under warranty, the profitability of the product is substantially lessened.
The industry has solved this problem by the use of various shipping inserts which restrain and protect the temperature sensing means or the switching means during transit. However, even though installation manuals and service manuals are written to specifically and emphatically instruct the installation personnel to remove the shipping insert, this removal does not always take place. In point of fact, one of the largest, if not the largest, sources of repair for newly installed thermostats is to have a separate service call during which the repairmen merely remove the shipping insert which should have been removed during installation. While this may seem elementary, many times in the haste of assembling a complete heat control system, perhaps including a furnace or air conditioner, the serviceman does not remove the shipping insert. This results in a thermostat which is totally unresponsive to the needs of the user.
Accordingly, it is an object of this invention to provide a thermostat which is suitable for calibration at the factory, may be shipped without concern for damage to the calibration, and which may be installed simply and efficiently in a manner which requires removal of the shipping insert prior to installation. Other objects will appear hereinafter.